New treatments that target the protein tau, a neuronal scaffolding protein that accumulates in neurodegenerative diseases including Alzheimer's (AD), are rapidly entering human clinical trials. Increasingly, clinical trials of such tau therapies are focusing on pure tauopathies, or disorders in which tau is causally- or strongly-linked to the underlying pathology in the absence of other toxic proteins such as beta amyloid. Pure tauopathies include corticobasal degeneration (CBD), progressive supranuclear palsy (PSP) and some variants of frontotemporal lobar degeneration (FTLD). Because CBD and PSP are clinically similar and share a common 4 microtubule binding repeat (4R) tau molecular pathology, clinical trials focused on these disorders may have better potential to demonstrate efficacy of tau-directed therapies than studies of more pathologically heterogeneous disorders such as AD and FTLD. However, new biomarkers are needed to assess the biological effects of tau-directed therapies in such 4R tauopathy human clinical trials. The most advanced biomarkers have been developed for AD clinical trials as part of the AD Neuroimaging Initiative (ADNI), and recently, a new project to develop similar measurements for FTLD (the FTLDNI) was funded. The overall goal of the project is to determine the most precise clinical, neuroimaging and biomarker methods for quantification of disease progression in 4R tauopathies for planning future phase II and III clinical trials. Taking advantage of the FTLDNI infrastructure already in place at UCSF, the proposed project will recruit 40 CBD subjects and 40 PSP subjects, and study each subject for one year using a combination of clinical measurements, fluid biomarkers and 3T MRI scans. Data from 120 normal control subjects acquired in parallel as part of the FTLDNI will be used for comparison. Individuals will undergo longitudinal clinical, oculomotor and MRI measurements at baseline, 6 and 12 months, as well as blood and CSF biomarker measurements at baseline and 12 months. The specific aims of the study are to 1) determine the most precise clinical rating scales for quantification of disease progression in 4R tauopathies; 2) identify which regions show the greatest longitudinal change in brain volume and cerebral perfusion; 3) identify the brain networks in which structural connectivity changes with disease progression; 4) quantify the longitudinal changes in saccade function in 4R tauopathies, 5) identify the neuroimaging correlates of longitudinal changes in motor and cognitive function, and activities of daily living in 4R tauopathies, and 6) quantify the longitudinal changes in Abeta42, CSF tau, phospho-tau and tau isoform ratios with disease progression. Should these aims be achieved, the proposed study would provide firm data about the best clinical, imaging and fluid biomarkers for following the course of disease in CBD and PSP, whether trials that combine CBD and PSP are feasible, and provide estimates from which power could be estimated for future clinical trials. All the data will eventually be available in a publicly accessible database for use by other researchers.